The present invention relates generally to a computerized method and system to aid radiologists in detection of asymmetric abnormalities in chest radiographs.
The present invention also generally relates to computerized techniques for automated analysis of digital images, for example, as disclosed in one or more of U.S. Pat. Nos. 4,839,807; 4,841,555; 4,851,984; 4,875,165; 4,907,156; 4,918,534; 5,072,384; 5,133,020; 5,150,292; 5,224,177; 5,289,374; 5,319,549; 5,343,390; 5,359,513; 5,452,367; 5,463,548; 5,491,627; 5,537,485; 5,598,481; 5,622,171; 5,638,458; 5,657,362; 5,666,434; 5,673,332; 5,668,888; 5,740,268; 5,790,690; 5,832,103; 5,873,824; 5,881,124; and 5,931,780 as well as U.S. patent application Ser. Nos. 08/173,935; 08/398,307 (PCT Publication WO 96/27846); Ser. No. 08/523,210 (PCT Publication WO 95/15537); Ser. Nos. 08/536,149; 08/562,087; 08/757,611; 08/900,191; 08/900,361; 08/900,362; 08/900,188; 08/900,189, 08/900,192; 08/979,623; 08/979,639; 08/982,282; 09/027,468; 09/027,685; 09/028,518; 09/053,798; 09/092,004; 09/098,504; 09/121,719; 09/131,162; 09/141,535; and 09/156,413; and U.S. provisional patent application No. 60/107,095, all of which are incorporated herein by reference. Of these patents and applications, U.S. Pat. Nos. 5,224,177; 5,359,513; Ser. Nos. 08/900,191; 08/900,362; 09/053,798; and No. 60/107,095 are of particular interest.
The present invention includes use of various technologies referenced and described in the above-noted U.S. Patents and Applications, as well as described in the references identified in the appended APPENDIX by the author(s) and year of publication andcross-referenced throughout the specification by numerals in brackets corresponding to the respective references listed in the APPENDIX, the entire contents of which, including the related patents and applications listed above and references listed in the APPENDIX, are incorporated herein by reference.
Detection of early lung cancers on chest radiographs is a difficult task for radiologists, because subtle lesions tend to be low in contrast and can overlap with ribs and clavicles. To assist radiologists in the detection of asymmetric abnormalities on digital chest radiographs, a novel contralateral subtraction technique has been proposed.[1] The contralateral subtraction technique is applied by subtracting a right/left reversed xe2x80x9cmirrorxe2x80x9d image from an original image, and symmetric skeletal structures such as ribs can be eliminated because the chest image of the right peripheral hemithorax is generally similar to that of the left hemithorax. With previous contralateral subtraction techniques, [1] 91% of contralateral subtraction images were rated as being of adequate, good, or excellent quality by use of a subjective evaluation method. However, misregistration errors were observed in nine of one hundred cases (i.e., 9%). These were mainly caused by the asymmetry of the posterior ribs on the right and left lungs. These asymmetric ribs on chest images are often caused by inappropriate positioning of a patient, and thus the locations and shapes of peripheral ribs in the mirror image appear different from those in the original image.
Another problem in the previous subtraction technique was that some minor misregistration errors were present in many of the subtraction images. This occurred because a global polynomial fitting technique was employed in the previous subtraction technique for smoothing of shift values over the entire lungs, and thus xe2x80x9ccorrectxe2x80x9d shift values in some locations were slightly degraded.
Accordingly, it is an object of the present invention to provide a method and system for warping two lungs of a mirror image as a preprocessing step prior to application of a contralateral subtraction technique so that rib structures in the mirror image become comparable to those in an original image.
It is another object of the present invention to provide a method and system for reducing misregistration errors by use of a localized smoothing technique, such as an elastic matching technique, for shift values.
These and other objects are achieved according to the present invention by providing a novel method, system and computer readable medium of computerized processing of chest images including obtaining digital first and second images of a chest and detecting rib edges in at least one of the first and second images. The rib edges are detected by correlating points in the at least one of the first and second images to plural rib edge models using a Hough transform to identify approximate rib edges in one of the images, and delineating actual rib edges derived from the identified approximate rib edges using a snake model. The method, system and computer readable medium further include deriving shift values using the actual rib edges and warping one of the first and second images to produce a warped image which is registered to the other of the first and second images based at least in part on the shift values.
According to another aspect of the present invention, there is provided a novel method, system and computer readable medium of computerized processing of chest images including obtaining digital first and second images of a chest, selecting template regions of interest (ROIs) in one of the first and second images and search area ROIs in the other of the first and second images, determining cross correlation values between pixels in the template ROIs and the search area ROIs, and determining of shift vectors for the template ROIs. The shift vectors are determined by determining local shift vectors between pixels in the search ROIs relative to the template ROIs, determining internal and external energies based on smoothness of the local shift vectors and the cross correlation values, respectively, and modifying the local shift vectors based at least in part on the internal and external energies. The method system and computer readable medium further include producing the shift vectors based on the modified local shift vectors and warping one of the first and second images to produce a warped image which is registered to the other of the first and second images based at least in part on the shift vectors.
The present invention further includes a computer readable medium storing program instructions by which the method of the invention can be performed when the stored program instructions are appropriately loaded into a computer, and a system for implementing the method of the invention.